Denitrification and desulfurization with elemental sulfur and hydrogen sulfide

Compared with conventional heterotrophic denitrification, sulfur-based autotrophic denitrification offers several advantages for the treatment of waters contaminated with nitrite or nitrate. First, it eliminates the needs for adding of organic carbons in the case of organic deficient wastewaters. Furthermore, the quantity of sludge produced under autotrophic conditions is substantially lower than that in a heterotrophic process which in turn reduces the cost associated with the treatment and digestion of the sludge. Desulfurization under denitrifying conditions is a suitable alternative for removal of H2S from contaminated gaseous streams because it eliminates the need of light energy input required for photoautotrophic desulfurization, and the supply of oxygen in aerobic chemolithotrophic desulfurization, in which simultaneous presence of both hydrocarbon gas and oxygen imposes a serious safety issue. In this work sulfur-based autotrophic denitrification and denitritation were studied in batch system using freely suspended cells and in a continuous biofilm reactor. Desulfurization of a H2S-containing gaseous stream under denitrifying conditions was studied in a semi-continuous packed bed reactor. Coleville enrichment, a mixed culture originated from a Canadian oil reservoir, which has the ability to function under both heterotrophic and autotrophic conditions, was used as the bacterial culture. The order of preference for electron donors used by the Coleville enrichment during the denitrification was established as: sulfide > biologically produced sulfur > acetate > elemental sulfur. Sulfate productions closely matched with theoretical values expected from stoichiometry in the batch experiments. Sodium bicarbonate functioned as an effective buffering agent and an inorganic carbon source during sulfur-based autotrophic denitrification. Strong inhibitory effect of nitrite on bacterial activity was observed. In the continuous biofilm reactor, sulfur-based nitrate removal rate increased linearly with the increase of nitrate loading rate through either an increase of feed flow rate or a variation of feed concentration. Similar trends were observed in the nitrite removal experiment. The highest nitrate removal rate (17.3 mM h-1) was obtained at a nitrate loading rate of 24.2 mM h-1 (corresponding residence time: 0.4 h) with a nitrate removal efficiency of 71.3% and a total nitrogen removal efficiency of 9.5%. The highest nitrite removal rate (13.2 mM h-1) was achieved at a nitrite loading rate of 18.0 mM h-1 (corresponding residence time: 0.6 h) with a nitrite removal percentage of 73.6%. The removal rates obtained in the present work were much higher than those reported in the literature. In the semi-continuous desulfurization experiments, the removal efficiency of H2S remained greater than 98.6% and 99.4% with nitrate and nitrite as the electron acceptor, respectively. The reduction rates of nitrate and nitrite increased with the increase of H2S loading rate through a variation of feed gas flow rate. The observed denitrification and denitritation rates were much higher than those obtained in the batch denitrification experiments with elemental sulfur and acetate

Improving Image Captioning by Leveraging Knowledge Graphs

We explore the use of a knowledge graphs, that capture general or commonsense knowledge, to augment the information extracted from images by the state-of-the-art methods for image captioning. The results of our experiments, on several benchmark data sets such as MS COCO, as measured by CIDEr-D, a performance metric for image captioning, show that the variants of the state-of-the-art methods for image captioning that make use of the information extracted from knowledge graphs can substantially outperform those that rely solely on the information extracted from images.Comment: Accepted by WACV'1

Engineering the energy gap near the valence band edge in Mn-incorporated Cu3Ga5Te9 for an enhanced thermoelectric performance

Cu3Ga5Te9-based compounds Cu3-xGa5MnxTe9 (x=0-0.2) with Mn substitution for Cu have been synthesized. The engineered energy gap (∆EA) between impurity and valence band is reduced from 44.4 meV at x=0 to 25.7 meV at x=0.1, which is directly responsible for the reduction of potential barrier for thermal excitation of carriers and enhancement in carrier concentration. However, the Seebeck coefficient shows an increasing tendency with the increasing of determined Hall carrier concentration (n). This anomalous behavior suggests that the Pisarenko plots under assumed effective masses do not fit the current relationship between the Seebeck coefficient and carrier density. With the combination of enhanced electrical conductivities and reduced thermal conductivities at high temperatures, the maximum thermoelectric (TE) figure of merit (ZT) of 0.81 has been achieved at 804 K with x=0.1, which is about 1.65 and 2.9 times the value of current and reported intrinsic Cu3Ga5Te9. The remarkable improvement in TE performance proves that we have succeeded in engineering the energy gap near the valence band edge upon Mn incorporation in Cu3Ga5Te9